Importance of junction functionality in highly crosslinked polymers

Barr-Howell, Barbara D.; Peppas, Nikolaos A.

doi:10.1007/bf00254215

Cited by 30 publications

(12 citation statements)

References 12 publications

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“…The equilibrium swelling ratio decreases with the increase of the cross-link functionality, as previously predicted. 30 However, the effect predicted is rather small. In the relaxed state, chains of gels with higher cross-link functionality are more stretched, and they tend to elongated to a less extent when the gels contact with solvent molecules.…”

Section: Resultsmentioning

confidence: 89%

A Molecular Theory of Polymer Gels

2002

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A new theory for polymer gels is developed on the basis of the single-chain mean-field (SCMF) theory. This theory takes the mesh chain or the star polymer as the characteristic unit of polymer gels, and it allows the study of chain conformation properties for gels in their different states. The preparation condition effect is conveniently described by the current theory, and the gels with complex chain structures can also be studied since the SCMF theory take realistic chain conformations into consideration. In this work, the theory is compared with the widely used Flory-type gel theory and with experimental observations. It is shown that the star polymer is a more natural basic unit of the gel structure. The current theory is found to provide a better description of the gels than the Flory-type theory as well as better agreement with gel swelling experimental data for poly(ethylene oxide) gels.

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Section: Resultsmentioning

confidence: 89%

A Molecular Theory of Polymer Gels

2002

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“…The number-average molecular weight between cross-links, M̄ c , was calculated using two methods: the Peppas−Merrill equation , and the Cima−Lopina equation . The Peppas−Merrill equation applies to swollen networks of cross-linked polymers prepared under conditions such that the cross-links were introduced in solution: …”

Section: Resultsmentioning

confidence: 99%

Poly(ethylene glycol) Star Polymer Hydrogels

1998

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Poly(ethylene glycol) (PEG) star polymer hydrogels were prepared by γ-irradiation of aqueous solutions of star PEG polymers. The swelling behavior of these gels in deionized water at 37 °C indicated that the gels prepared from PEG star polymers with a small number of long arms swelled to a greater extent than those prepared from PEG star polymers with a large number of short arms. PEG star polymers and branched PEG polymers were modified to incorporate acrylate groups on the ends of the polymer arms. These acrylated star or branched polymers were copolymerized with poly(ethylene glycol) diacrylate in the presence of UV light. The ensuing materials swelled to a greater extent than hydrogels prepared without acrylated star or branched PEG polymers. Number-average molecular weights were calculated using several rubber elasticity-based theories.

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“…This hypothesis was examined using an analysis based on a modified version of the Flory−Rehner description of the equilibrium swelling of polymer gels cross-linked in the solid state . This modified description of the equilibrium swelling behavior includes the effects of a non-Gaussian chain length distribution (appropriate for the highly cross-linked PEG−AA networks), chain ionization, and composition-dependent structural factor A φ : − The parameter M c is the theoretical value of the molecular weight between cross-links, υ is the specific volume of the polymer, V 1 is the molar volume of the penetrant, M n is the number-average molecular weight of the linear chains in the absence of cross-links (≈75 000 for multiacrylate polymer systems), υ 2,s is the polymer volume fraction in the swollen state, and χ is the Flory polymer−solvent interaction parameter. The term which appears on the right-hand side of eq 6 and contains the pH of the swelling agent and the dissociation constant, K a , of the polyacid accounts for the ionic contribution to swelling.…”

Section: Resultsmentioning

confidence: 99%

Compositional Effects on Network Structure of Highly Cross-Linked Copolymers of PEG-Containing Multiacrylates with Acrylic Acid

Scott

Peppas

1999

Macromolecules

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Novel ionizable polymer networks were prepared from oligo(ethylene glycol) (OEG) multiacrylates and acrylic acid (AA), employing bulk radical photopolymerization techniques. The properties of these materials exhibit a complex dependence on the network structure and composition. Dynamic mechanical analysis and penetrant sorption experiments demonstrated that the cross-linked structure of the materials depends very strongly on the AA content, even in cases where the network chain population is expected to be composed solely of ethylene glycol oligomers. The results indicate that interchain interactions are diminished as the AA content is increased, due to the increased spatial separation of OEG chains. The compositional dependence of the glass transition temperature is qualitatively described by a treatment consistent with that employed for polymer blends, and deviations from ideal blend behavior point to the importance of system-specific free volume changes during the radical polymerization process. Hence, the glass transition temperature and other network properties are closely coupled to the polymerization kinetics.

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Importance of junction functionality in highly crosslinked polymers

Cited by 30 publications

References 12 publications

A Molecular Theory of Polymer Gels

A Molecular Theory of Polymer Gels

Poly(ethylene glycol) Star Polymer Hydrogels

Compositional Effects on Network Structure of Highly Cross-Linked Copolymers of PEG-Containing Multiacrylates with Acrylic Acid

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